Equallogic: Seamless Upgrade

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We’ve had (2) Equallogic PS100s for at least 5+ years that Dell was discontinuing support in April as well as beginning to run low on storage; we used this as an opportunity to upgrade to a new 6100E, couldn’t be happier with our decision. Anyone using Equallogic knows they build a strong product from a hardware and software perspective, couple that with their excellent assortment of tools for VMWare integration and you have a very solid SAN solution for a medium business. As proof, minus the occasional drive failure we had ZERO production-impacting issues with these units in almost 5+ years of use, I think that is pretty impressive. Our drive failures actually went down as well as we continued to climb in firmware versions.

The migration process from our PS100s was seamless and was accomplished without any service interruption thanks to storage vmotion. We followed the below process:

  • Racked new unit, connected to our SAN switches, set IPs and configuration on unit.
  • Created new volumes, assigned access rights based on IQN and presented to our VMWare cluster via group IP.
  • Created datastores from the volumes.
  • Began storage vmotion of VMs, once completed, remove all old datastores/iSCSI configuration.

We did run into an interesting “issue” at first that we thought was an issue. On our PS100s we always had 4 active paths (using Equallogic Multipathing plugin), after moving to the PS6100E we noticed we were only seeing 2 active paths for each datastore. We used setup.pl to modify the 3 session variables to no avail. After working with high level Equallogic engineers we discovered that in firmware v6+ and beyond they have changed the way the multipathing process works. Now the array calculates the total number of physical iSCSI NICs you have and only allows that number of connections, modifying the plugin session variables will not change this behavior so they are basically useless; control has been shifted from the plugin to the array. A bit more official from our Dell engineer:

The new firmware is designed to limit the number of connections in order to prevent saturation of sessions. The new firmware is more aggressive at limiting number of sessions that are created. When creating sessions between the host and member, it will not create more than either the host or member NICs can fill. The array will limit the total number of MPIO sessions created by ALL hosts to prevent exceeding the pool limits; logic will keep the total number of sessions at 90% of the pool limit.

Example 1: host has 2x1Gb NICs, connecting to a 2 member quadfather group. Even if the user sets the desired sessions higher, the multipathing tools won’t create more than 2 sessions to each member, since that would fill the pipe on the host.

Posting this for the benefit of others, highly recommended to our Equallogic engineer that they document this somewhere besides internal Dell documents! A simply NOTE on the download page would be nice!

So far though, minus this firmware change, we have had ZERO issues with our new unit and have seen our queue depth and latencies decrease pretty significantly. Watch for another blog post where I will present some of our SANHQ data from our PS100s and from our PS6100E!

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Author: Travis Kensil

Director of IT. Husband and father. Michigan beachbum.

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